Ejector

ABSTRACT

An ejector having a nozzle portion having openings provided at a distal end and a proximal end thereof, respectively, for injecting drive-stream gas, a diffuser portion provided on a distal end side of the nozzle portion for drawing in auxiliary gas by negative pressure which is generated in the drive-stream gas by injection from the nozzle portion so as to join the auxiliary-stream gas together with the drive-stream and discharge the drive-stream gas and the auxiliary gas, a needle slidably inserted into an interior of the nozzle portion in an axial direction of the nozzle portion for adjusting an opening area of the nozzle portion in accordance with an inserted position thereof, a drive unit for moving the needle axially and an auxiliary stream introducing portion comprising at least two openings for introducing the auxiliary-stream gas into the diffuser portion therefrom.

The present invention claims foreign priority to Japanese patentapplication No. P.2005-092325, filed on Mar. 28, 2005, the contents ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ejector which has a configuration inwhich an auxiliary-stream gas is made to join a drive-stream gas fordischarge the drive-stream gas and the auxiliary-stream gas therefrom.

2. Description of the Background Art

There has been proposed a technique in which an ejector is used as ahydrogen circulating pump in a fuel cell system. The ejector is such asto have a construction in which circulating hydrogen is drawn in forre-supply by making use of negative pressure produced by injecting ahigh-pressure fluid from a jet nozzle.

When the ejector so constructed is used, the circulating capability islimited by the diameter of the jet nozzle, and hence, there occurs acase where the ejector is not suitable for a fuel cell system having alarge flow rate range such as one for a motor vehicle.

On the contrary, Japanese Patent Unexamined Publication No.JP-A-8-338398 proposes a technique in which the opening area of aninjection nozzle is adjusted by axially moving a cylindrical adjustingrod (a needle).

Incidentally, depending on the production accuracy of constituentcomponents of an ejector such as a needle and its guide member or anactuator for moving the needle, a needle set in a nozzle is caused todeviate minutely from an axial direction thereof. In the event that aconfiguration such as seen in the aforementioned technique is adoptedfor the ejector like this in which an auxiliary-stream gas is caused tosimply hit the needle, there is caused a problem in the drawing forceand drawing amount of the auxiliary stream.

The problem will be described using FIGS. 4, 5. FIGS. 4 and 5 aredrawings which illustrate a main part of a conventional ejector todescribe the problem inherent therein. Firstly, in the event that adistal end portion of a needle 33 is displaced in a direction in whichthe distal end portion moves away from an auxiliary-stream gas (namely,in a direction which follows an arrow A in FIG. 4), an opening area of alocation of a distal end portion of a nozzle 32 which lies near theauxiliary-stream gas (namely, a lower region of the distal end portionof the nozzle 32) is increased. As a result, a drawing force exerted onthe auxiliary-stream gas by a driven steam of gas is increased, wherebythe flow rate of the auxiliary-stream gas is increased excessively(refer to FIG. 4).

In contrast, in the event that the distal end portion of the needle 33is displaced in a direction in which the distal end portion approachesthe auxiliary-stream gas (namely, in an opposite direction to an arrow Ain FIG. 5) due to the pressure of the auxiliary-stream gas, an openingarea of a location of the distal end portion of the nozzle which liesaway from the auxiliary-stream gas (namely, an upper region of thedistal end portion of the nozzle 32) is increased. As a result, thedrawing force exerted on the auxiliary-stream gas by the drive-streamgas is decreased, whereby the flow rate of the auxiliary-stream gas isdecreased excessively (refer to FIG. 5).

Thus, there exists a problem where an accurate control of the drawingforce and drawing amount of the auxiliary-stream gas becomes difficultto be implemented. In particular, in a case where an ejector isinstalled in a fuel cell system in which an unreacted off-gas iscirculated, the unreacted off-gas constitutes an auxiliary stream, andsince the flow rate and flow velocity of the auxiliary stream can affectpower generating conditions, controlling the flow rate and flow velocityof the auxiliary stream becomes crucial to secure a desired powergeneration performance, as well. While it is considered as a means forattaining this to configure the needle to follow precisely the axisthereof in a perfect fashion when it slides, there is caused a problemwhere since a severe accuracy which is required for productiondeteriorates the productivity, the attempt is unrealistic.

SUMMARY OF THE INVENTION

Consequently, an object of the invention is to provide an ejector whichcan control the flow rate and flow velocity of the auxiliary-stream gaswith good accuracy.

According to a first aspect of the invention, there is provided anejector comprising:

a nozzle portion (for example, a nozzle 32 in an embodiment which willbe described later on) having openings provided at a distal end and aproximal end thereof, respectively, for injecting drive-stream gas;

a diffuser portion (for example, a diffuser 31 in the embodiment whichwill be described later on) provided on a distal end side of the nozzleportion for drawing in auxiliary gas by negative pressure which isgenerated in the drive-stream gas by injection from the nozzle portionso as to join the auxiliary-stream gas together with the drive-streamand discharge the drive-stream gas and the auxiliary gas;

a needle (for example, a needle 33 in the embodiment which will bedescribed later on) slidably inserted into an interior of the nozzleportion in an axial direction of the nozzle portion for adjusting anopening area of the nozzle portion in accordance with an insertedposition thereof;

a drive unit (for example, a solenoid 11 in the embodiment) for movingthe needle axially; and

an auxiliary stream introducing portion (for example, anauxiliary-stream gas introducing portion 13 in the embodiment)comprising at least two openings for introducing the auxiliary-streamgas into the diffuser portion therefrom.

According to the first aspect of the invention, since theauxiliary-stream gas is introduced from at least two openings in theauxiliary stream introducing portion, the auxiliary-stream gas isallowed to be introduced from a plurality of directions relative to theneedle, and as a result, the pressure exerted on the needle from theauxiliary-stream gas can be dispersed relative to the axial direction ofthe needle. Consequently, deviations in drawing force and drawing amounttriggered by the deviation of the needle from the axial directionthereof can be suppressed, whereby since the opening area and openingregion of the nozzle portion can be maintained in originally designedstates, the drawing force and drawing amount of the auxiliary-stream gascan be controlled with good accuracy without being affected by thedeviation of the needle from the axial direction thereof.

According to a second aspect of the invention, as set forth in the firstaspect of the present invention, it is preferable that the ejectorfurther comprising a buffer chamber provided on an upstream side of theauxiliary stream introducing portion,

wherein the auxiliary-stream gas is adopted to be introduced into theplurality of openings from the buffer chamber.

According to the structure, since an auxiliary-stream gas can bedistributed to each of the openings via the buffer chamber withouthaving to have a configuration in which piping is individually connectedto each auxiliary stream introducing portion, auxiliary-stream gas caneasily be supplied to the diffuser portion from multiple directions.

According to a third aspect of the invention, as set forth in the firstaspect of the present invention, it is preferable that the ejector isused on a fuel cell system.

According to the structure, since the drawing force and drawing amountof auxiliary-stream gas can be controlled with good accuracy regardlessof the shaft position of the needle, an easy and fine control of theflow of fuel cell system gas can be implemented, whereby the powergeneration stability of the fuel cell can be enhanced.

According to a fourth aspect of the present invention, as set forth inthe first aspect of the present invention, it is preferable that theopenings of the auxiliary stream introducing portion are arranged alongwith a circumferential direction of the diffuser portion.

According to a fifth aspect of the present invention, as set forth inthe first aspect of the present invention, it is preferable that theopenings of the auxiliary stream introducing portion are arranged inpoint symmetry manner relative to a central axis of the needle.

According to the first aspect of the invention, since the opening areaand opening region of the nozzle portion can be maintained in theoriginally designed states, the drawing force and drawing amount of theauxiliary-stream gas can be controlled with good accuracy.

According to the second aspect of the invention, the auxiliary-streamgas can easily be supplied to the diffuser portion from multipledirections.

According to the third aspect of the invention, the power generationstability of the fuel cell can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing which illustrates the configuration of a fuel cellsystem which includes a variable flow rate ejector according to anembodiment of the invention;

FIG. 2 is a side sectional view of the variable flow rate ejectoraccording to the embodiment of the invention;

FIG. 3 is an explanatory drawing which illustrates the flow ofauxiliary-stream gas of the variable flow rate ejector according to theembodiment of the invention;

FIG. 4 is a drawing depicting a main part of a conventional ejectorwhich illustrates a problem inherent therein; and

FIG. 5 is a drawing depicting the main part of the conventional ejectorwhich illustrates a problem inherent therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a variable flow rate ejector according to an embodiment ofthe invention will be described by reference to the accompanyingdrawings. FIG. 1 is a drawing which shows the configuration of a fuelcell system 20 including a variable flow rate ejector 10 according anembodiment of the invention, and FIG. 2 is a side sectional view of thevariable flow rate ejector 10 according to the embodiment of theinvention. The variable flow rate ejector 10 according to the embodimentof the invention is provided in the fuel cell system 20 which isinstalled on a vehicle such as an electric vehicle, and this fuel cellsystem 20 is made up of the variable flow rate ejector 10, fuel cells21, an oxidant supply unit 24, a heat exchanger 25 and a water separator26.

The fuel cell 21 is made up of a stack which includes a plurality ofstacked cells, each formed by holding a solid polymer electrolytemembrane, which is, for example, a solid polymer ion exchange membraneby an anode and a cathode from both sides thereof and includes a fuelelectrode to which, for example, hydrogen is supplied as a fuel; and anair electrode to which, for example, air containing oxygen is suppliedas an oxidant.

An air supply port 21 a into which air is supplied from the oxidantsupply unit 24 and an air discharge port 21 b having provided therein anair discharge valve 28 for discharging air or the like in the airelectrode to the outside are provided on the air electrode. On the otherhand, a fuel supply port 21 c to which hydrogen is supplied and a fueldischarge port 21 d for discharging hydrogen or the like in the fuelelectrode to the outside are provided on the fuel electrode.

The oxidant supply unit 24 is made up of, for example, a compressor andis controlled in response to a load applied to the fuel cell 21, aninput signal from an accelerator pedal (not shown) and the like, so asto supply air to the air electrode of the fuel cell 21 via the heatexchanger 25. The heat exchanger 25 cools air sent from the oxidantsupply unit 24 down to a predetermined temperature for supply to thefuel cell 21.

Hydrogen, which functions as fuel, is supplied from the fuel supply port21 c to the fuel electrode of the fuel cell 21 via the variable flowrate ejector 10. Furthermore, a discharged fuel which is discharged fromthe fuel discharge portion 21 d of the fuel cell 21 is introduced intothe variable flow rate ejector 10 through a check valve 29 after wateris removed therefrom at the water separator 26, and as will be describedlater on, fuel and the discharged fuel discharged from the fuel cell 21are made to join or mix with each other for supply to the fuel cell 21.Note that water separated from the discharged fuel at the waterseparator 26 is discharged to the outside by opening a drain valve 30.

The variable flow rate ejector 10 according to the embodiment of theinvention is such as to make a discharged fuel circulated from the fuelcell 21 join a stream of fuel gas supplied from the fuel supply unit 22by making use of the stream of fuel gas so supplied and to control theflow rate of fuels supplied to the fuel cell 21 based on an air pressurePair on the air electrode side of the fuel cell 21 which is detected bya pressure sensor 7 and a fuel pressure Pfuel on the fuel electrode sideof the fuel cell 21 which is detected by a pressure sensor 6 whenreceiving a control instruction from an ECU 5 and is configured toinclude, as shown in FIG. 2, a diffuser 31, a nozzle 32 and a needle 33.

A fluid passageway 43 is formed in the diffuser 31 in such a manner asto penetrate axially the diffuser 31 on a downstream side thereof. Thefluid passageway 43 has a throat portion 44 where an inside diameterthereof becomes minimum at a position along the length thereof, and athrottle portion 45 is provided upstream of the throat portion 44 whichhas an inner circumferential surface which diametrically contractsgradually and continuously as it proceeds downstream, and adiametrically expanding portion 46 is provided downstream of the throatportion 44 which has an inner circumferential surface whichdiametrically expands gradually and continuously as it proceedsdownstream.

The nozzle 32 is provided in an interior of the diffuser 31 in such amanner as to protrude coaxially with the diffuser 31 towards an upstreamside of the fluid passageway 43.

A fluid passageway 51 is formed in an interior of the nozzle 32 in sucha manner as to extend along an axial direction of the nozzle 32. Aninner circumferential surface 32A, which constitutes a wall surface ofthe fluid passageway 51, is formed at a distal end portion of the nozzle32 in such a manner as to diametrically contract gradually andcontinuously towards a distal end side thereof (a downstream side of thefluid passageway 51). A downstream end of the fluid passageway 51continues to an opening 52 which opens at a distal end face 32 b of thenozzle 32, and an upstream end of the fluid passageway 51 is blocked upby a diaphragm (not shown). A fuel supply pipe (not shown) is connectedto the fluid passageway 51 for introducing therein to fuel supplied fromthe fuel supply unit 22.

The needle 33 is inserted into the interior of the nozzle 32 coaxiallywith the nozzle 32, and the needle 33 is held by a needle holding guide(not shown) in such a manner as to slide in an axial direction which iscoaxial with the nozzle 32. Here, an outer circumferential surface ofthe needle 33 is formed at a distal end portion of the needle 33 in sucha manner as to diametrically contract gradually and continuously as itextends towards a distal end side thereof. Namely, when the needle 33slides in the axial direction in the interior of the nozzle 32, aprotruding amount of the distal end portion of the needle 33 whichprotrudes from the opening 52 of the nozzle 32 is changed. Inassociation with this, an opening area of a gap between the innercircumferential surface of the nozzle 32 and the outer circumferentialsurface of the needle 33 is changed, whereby the flow rate of fuel thatis injected into an auxiliary stream chamber 48 from the opening 52 ofthe nozzle 32 can be adjusted.

Note that the needle holding guide, which holds the needle 33 in such amanner as to slide relative to the axial direction, is formed into, forexample, an annular disc shape having an appropriate through holethrough which fluid can pass, and the needle 33 is inserted through aneedle insertion hole which penetrates the annular disc in the axialdirection. In addition, the needle 33 is connected electrically andmechanically to a solenoid 11, so that the needle 33 is configured to bemoved back and forth in the axial direction in response to ON/OFFoperations of the solenoid 11.

Additionally, an auxiliary-stream gas introducing portion 13 having aplurality of auxiliary-stream gas introducing holes 12 is formed in theauxiliary stream chamber 48 at a location which faces the outercircumferential surface of the nozzle 32. This auxiliary-stream gasintroducing portion 13 is connected to an auxiliary stream introducingpipe 49, which communicates with a fuel off-gas discharge path, via abuffer chamber 14 which is formed on an outer circumferential side ofthe auxiliary-stream gas introducing portion 13. For an example, asshown in FIG. 2, pluralities of the auxiliary stream gas introducingholes 12 are arranged along with a circumferential direction of thediffuser 31.

The fuel cell system 20 including the variable flow rate ejector 10according to the embodiment of the invention is configured as has beendescribed heretofore. Next, the operation of the variable flow rateejector 10 will be described. FIG. 3 is an explanatory drawing whichillustrates the flow of an auxiliary-stream gas in the variable flowrate ejector according the embodiment of the invention.

In this variable flow rate ejector 10, a discharged fuel gas from thefuel cell 21 is supplied therein to from the auxiliary streamintroducing pipe 49 through the plurality of auxiliary-stream gasintroducing holes 12 possessed by the auxiliary-stream gas introducingportion 13 via the buffer chamber 14. In addition, a fuel is suppliedinto the fluid passageway 51 in the interior of the nozzle 32 from thefuel supply pipe (not shown). Then, the fuel so supplied is injectedfrom the opening 52 of the nozzle 32, that is, the gap between thenozzle 32 and the needle 33 towards the fluid passageway 43 of thediffuser 31. As this occurs, negative pressure is produced in thevicinity of the throat portion 44 of the diffuser 31 where ahigh-velocity fuel stream passes, and fuel auxiliary-stream gas withinthe auxiliary stream chamber 48 is drawn into the fluid passageway 43 bythe vacuum so produced, so as to be mixed with the fuel injected fromthe nozzle 32 for discharge from a downstream end of the diffuser 31,whereby the discharged fuel discharged from the fuel cell 21 iscirculated via the variable flow rate ejector 10.

Thus, since the auxiliary-stream gas (in this case, the discharged fuelgas) is introduced individually from the plurality of auxiliary-streamgas introducing holes 12, the auxiliary-stream gas is introduced from aplurality of directions relative to the needle 33. As a result, apressure that the needle 33 receives from the auxiliary-stream gas canbe dispersed relative to the axial direction. Consequently, thedeviation in drawing force and drawing amount of auxiliary stream thatis triggered by the deviation of the needle 33 from the axial directionthereof can be suppressed, whereby since the opening area and openingregion of the nozzle 32 can be maintained in the originally designedstates, even in the event that the needle 33 is caused to deviateslightly from the axial direction thereof, the drawing force and drawingamount of auxiliary-stream gas can be controlled with good accuracy.

In addition, since the auxiliary-stream gas can be distributedindividually to the plurality of auxiliary-stream gas introducing holes12 via the buffer chamber 14, the auxiliary-stream gas can easily besupplied to the diffuser 31 from multiple directions. For an example,the auxiliary-stream gas introducing holes 12 are disposed in pointsymmetry relative to a central axis of the needle 33, whereby theauxiliary-stream gas is dispersed, so as to hit the needle 33 not onlyfrom the multiple direction but also in substantially the same amount,thereby making it possible to obtain an advantage where the deviation inposition of the needle 33 can be suppressed. The advantage can beachieved by arranging the auxiliary-stream gas introducing holes 12along with the circumferential direction of the diffuser 31, asdescribed above.

In addition, by applying the ejector 10 to the fuel cell system, an easyand fine control of the stream of fuel cell system gas can beimplemented, whereby the power generation stability of the fuel cell canbe enhanced. Note that a space for the water separator 26 or the like issecured upstream of the ejector 10, even in the event that the bufferchamber 14 is configured to be provided in the ejector 10, an effectresulting from a reduction in sucking amount can be suppressed.

Thus, as has been described heretofore, according to the ejector of theembodiment of the invention, the control of drawing force and drawingamount of auxiliary-stream gas can be implemented with good accuracy.

Note that the contents of the invention are, of course, not limited tothe embodiment. For example, while in the embodiment, the ejector isdescribed as being applied to the fuel cell system, the ejector can beapplied to other systems.

While there has been described in connection with the preferredembodiments of the present invention, it will be obvious to thoseskilled in the art that various changes and modification may be madetherein without departing from the present invention, and it is aimed,therefore, to cover in the appended claim all such changes andmodifications as fall within the true spirit and scope.

1. An ejector comprising: a nozzle portion having openings provided at adistal end and a proximal end thereof, respectively, for injectingdrive-stream gas; a diffuser portion provided on a distal end side ofthe nozzle portion for drawing in auxiliary gas by negative pressurewhich is generated in the drive-stream gas by injection from the nozzleportion so as to join the auxiliary-stream gas together with thedrive-stream and discharge the drive-stream gas and the auxiliary gas; aneedle slidably inserted into an interior of the nozzle portion in anaxial direction of the nozzle portion for adjusting an opening area ofthe nozzle portion in accordance with an inserted position thereof; adrive unit for moving the needle axially; and an auxiliary streamintroducing portion comprising at least two openings for introducing theauxiliary-stream gas into the diffuser portion therefrom.
 2. The ejectoras set forth in claim 1, further comprising a buffer chamber provided onan upstream side of the auxiliary stream introducing portion, whereinthe auxiliary-stream gas is adopted to be introduced into the pluralityof openings from the buffer chamber.
 3. The ejector as set forth inclaim 1, wherein the ejector is used on a fuel cell system.
 4. Theejector as set forth in claim 1, wherein the openings of the auxiliarystream introducing portion are arranged along with a circumferentialdirection of the diffuser portion.
 5. The ejector as set forth in claim1, wherein the openings of the auxiliary stream introducing portion arearranged in point symmetry manner relative to a central axis of theneedle.